Semiconductor device and method of manufacturing semiconductor device

Abstract

A semiconductor device includes thin film transistors each having an oxide semiconductor. The oxide semiconductor has a channel region, a drain region, a source region, and low concentration regions which are lower in impurity concentration than the drain region and the source region. The low concentration regions are located between the channel region and the drain region, and between the channel region and the source region. Each of the thin film transistors has a gate insulating film on the channel region and the low concentration regions, an aluminum oxide film on a first part of the gate insulating film, the first part being located on the channel region, and a gate electrode on the aluminum oxide film and a second part of the gate insulating film, the second part being located on the low concentration regions.

What is claimed is: 
     
       1. A method of manufacturing a semiconductor device with a thin film transistor having an oxide semiconductor which includes a channel region, a drain region, a source region, and low concentration regions which are lower in impurity concentration than the drain region and the source region, the low concentration regions being located between the channel region and the drain region, and between the channel region and the source region, comprising steps of:
 selectively forming a semiconductor layer of the thin film transistor on a substrate; 
 forming a gate insulating film so as to cover the semiconductor layer; 
 forming an aluminum oxide film on the gate insulating film; 
 selectively patterning the aluminum oxide film so as to be locate on the channel region; 
 forming a gate electrode on the gate insulating film and on the aluminum oxide film selectively patterned; 
 selectively patterning the gate electrode so as to be located on the aluminum oxide film selectively patterned and on the low concentration regions; and 
 performing ion implantation by using the gate electrode selectively patterned as a mask. 
 
     
     
       2. The method of manufacturing the semiconductor device according to  claim 1 , further comprising steps of:
 forming an insulating film so as to cover the gate electrode selectively patterned and the gate insulating film; 
 forming contact holes in the insulating film and the gate insulating film in such a manner that the drain region and the source region are exposed; and 
 forming wirings in the contact holes. 
 
     
     
       3. The method of manufacturing the semiconductor device according to  claim 1 ,
 wherein a film thickness of the aluminum oxide film is 5 nm to 20 nm. 
 
     
     
       4. The method of manufacturing the semiconductor device according to  claim 1 ,
 wherein a step of forming the gate electrode on the gate insulating film includes an annealing treatment. 
 
     
     
       5. The method of manufacturing the semiconductor device according to  claim 4 ,
 wherein the gate electrode sucks up the oxygen in the drain region, the source region, and the low concentration regions with the annealing treatment.